The loss rate will decrease as the water level approaches the leak level. When I had a deep end leak I watched the level vs. time, accurately, to see if it was slowing and in my case it wasn't so I started looking at the deep end. You said the level is below the skimmers but if it's still above the returns just plug the returns and see what happens. Save the cost of a pressure test. What about the light itself? If you want to proceed to the next step, dye testing, I can give you some hints. Have to run for a bit but will check back a little later.
Al